This invention relates to a method and apparatus for fabricating light management films and in particular to such films fabricated from randomly or pseudo randomly mastered surfaces.
In backlight computer displays or other systems, films are commonly used to direct or diffuse light. For example, in backlight displays, brightness enhancement films use prismatic or textured structures to direct light along the viewing axis (i.e., normal to the display), which enhances the brightness of the light viewed by the user of the display and which allows the system to use less power to create a desired level of on-axis illumination. Films for turning light can also be used in a wide range of other optical designs, such as for projection displays, traffic signals, and illuminated signs. Backlight displays and other systems use layers of films stacked and arranged so that the prismatic or textured surfaces thereof are perpendicular to one another and are sandwiched between other optical films known as diffusers. Diffusers have highly irregular or randomized surfaces.
Textured surfaces have been widely used in optical applications such as backlight display films, diffusers, and rear reflectors. In a wide range of optical designs it is necessary to use microstructures to redirect and redistribute light (or diffuse light) to enhance brightness, diffusion, or absorption. For example, in a backlight display system it is often required to both direct the illumination incident on a screen toward a direction normal to the screen and to spread the illumination over the viewer space. Performance of thin-film solar cells can be markedly improved by light trapping based on textured TCO/glass/metal substrates, and angle selective specular reflectors. Microstructures are sometimes randomized for reducing manufacturing defects such as pits and defects from optical interference between two components such as moiré pattern, speckle and Newton's ring. Ideally, an optical film, instead of two or more films together, should have both the performance of brightness enhancement and least defects.
In backlight applications brightness enhancement films and diffuser films are commonly combined as part of a display screen to redirect and redistribute light. In the prior art a typical solution for enhancing brightness is to use an optical film having a surface structured with linear prisms. For example, the prior art describes using a prismatic film to enhance the on-axis brightness of a backlight liquid crystal display. To hide manufacturing defects and decrease the optical coupling, an optical film with structures randomly varying in height along its length direction has been crafted to achieve brightness enhancement while hiding manufacturing defects and reducing optical coupling between two sheets of such film.